In order to provide a more compact format for identifying mixtures of refrigerants in the following discussions, mixtures of refrigerants will be listed in the form of: EQU R-ABC/DEF/GHI N0/N1/N2
which represents a mixture of refrigerants (fluids) R-ABC, R-DEF, and R-GHI where N0, N1, and N2 are the weight percentages of each component refrigerant fluid, and N0+N1+N2=100 percent; or in the form of: EQU R-ABC/DEF/GHI N0--N0'/N1--N1'/N2--N2'
which is similar, but specifies ranges of the weight percentages each of the component refrigerant fluids, with the total of the weight percentages being 100 percent.
Zeotropic (nonazeotropic) mixtures of refrigerants will change composition if they are allowed to leak as vapor phase from a container containing all components of the refrigerant mixture in both vapor and liquid phases. Single component and azeotropic mixtures of refrigerants do not change composition appreciably from vapor leakage. Single component and azeotropic mixtures of refrigerants have only one boiling point temperature for a given pressure, provided the refrigerant exists as both liquid and vapor states in the container. Zeotropic mixtures of refrigerants will boil over a range of temperatures at a given pressure. As the temperature is raised, the point at which the first bubbles appear (constant pressure) in the liquid is known as the "bubble point," which is roughly analogous to the boiling point of a single component or an azeotropic mixture. Starting in a vapor phase and lowering the temperature (at a constant pressure) to the point where the first droplet of liquid forms defines what is known as the "dew point" of the mixture of refrigerants. The difference between the bubble point temperature and the dew point temperature is known as the temperature "glide". A pressure gauge connected to a cylinder containing a zeotropic mixture of refrigerants will read the bubble point pressure for the corresponding temperature of the refrigerant mixture.
Under the Montreal Protocol, as amended, United States laws (1990 Clean Air Act), and U.S. Environmental Protection Agency rules, the production and importing of dichlorodifluoromethane (CFC-12 or R-12) refrigerant ended on Dec. 31, 1995. Additionally, only 15% of the 1989 baseline amounts of chlorinated fluorocarbons (CFCs) was allowed to be produced or imported into the U.S. during the year 1995, adjusted on an ozone depletion factor basis. R-12 was the major share of that production.
With the effective date of the ban on U.S. R-12 production and importing having passed (Dec. 31, 1995), one industry option has been to retrofit R-12 refrigeration or air conditioning systems, both stationary and automotive, to R-134a (tetrafluoroethane). The mineral oils used in R-12 systems are completely immiscible in R-134a. The industry has therefore developed new oils, which are either polyalkylene glycol (PAG) based (for automotive) or polyol ester (POE) based (stationary refrigeration and some automotive retrofit).
While PAG oils are good lubricants, and are miscible in R-134a at typical evaporator temperatures, they have two main problems. First, most PAG oils cannot tolerate even minute traces of residual chlorides that remain in the R-12 refrigeration or air conditioning systems that have been purged of R-12. These chlorides are dissolved in the small amount of mineral oils which cannot be flushed out or are in coatings on the inside of aluminum piping (aluminum chloride from previous R-12) or are dissolved in rubber hoses. The presence of chlorides greatly accelerates the breakdown of most PAG oils.
It has been reported in the literature that test systems that were flushed with R-11 (trichlorofluoromethane) and then retrofitted to PAG oil and R-134a, sustained catastrophic compressor failures within one week due to oil breakdown. R-11 has a greater affect on PAG oil breakdown than does R-12. It was common practice in the automotive air conditioning service industry, into the early 1990s, to flush R-12 systems with R-11 to remove contaminates. The traces of R-11 remaining do not interfere with R-12 operation, but could cause premature failures if R-12 systems are ever retrofitted to R-134a and PAG oils.
Compressors manufactured for R-12 and mineral oil use were often constructed with a paraffin based wax coating on the motor windings as an aid to building the motor without breaking the wire during the motor winding phase of the construction. When retrofitted to R-134a and POE oils, the paraffin would sometimes come off the windings, and not dissolve in the R-134a refrigerant and POE oils, and circulate through the system as solids and plug up the refrigerant metering device, usually a capillary tube, causing the system to fail. R-12 (or a substitute with adequate mineral oil miscibility) and mineral oil just dissolve the pieces of paraffin wax that come off the motor windings and therefore do not clog the refrigerant metering device.
Finally, the low critical temperature of R-134a (214.07 degrees Fahrenheit) verses the critical temperature of R-12 (233.26 degrees Fahrenheit) can cause abnormally high head pressures in hot ambient conditions in systems designed for R-12. For automotive applications, stopped traffic or hot climates can cause a reduction in R-134a performance. Systems designed for R-134a often increase the size of the condenser about 50 percent over the size similarly designed R-12 system condenser. Stationary systems, such as vending machines, now retrofitted to R-134a, may see high head pressure and low performance problems when the condenser becomes slightly fouled by dirt and dust. R-12 systems can run much longer between cleanings to remove dust and dirt from the condenser than similar systems converted to R-134a.
R-406A is a known ternary mixture of refrigerants, consisting of isobutane (R-600a), chlorodifluoroethane (R-142b), and chlorodifluoromethane (R-22), that provides a "drop-in" substitute for dichlorodifluoromethane (R-12) refrigerant. R-406A is described in U.S. Pat. Nos. 5,151,207 and 5,214,929, the disclosures of which are incorporated herein by reference.
If one must convert an existing R-12 refrigeration or air conditioning system to another refrigerant due to the Montreal Protocol mandated phaseout of R-12 refrigerant, it is usually far preferable to use a refrigerant mixture with adequate miscibility with mineral oils used by R-12 systems, such as R-406A (R-600a/142b/22 4/41/55) or GHG-X4 (R-600a/124/142b/22 4/28.5/16.5/51) than to attempt to retrofit to R-134a. However, one may have followed the industry recommended choice and already retrofitted said systems to R-134a or purchased a new system that was manufactured for R-134a refrigerant, using lubricants that are miscible with R-134a such as POE or PAG oils.
To date, the oils used in new or retrofitted R-134a refrigeration and air conditioning systems (PAG and some POE) are adversely affected by chlorinated refrigerants (HCFCs), with the PAG oils being affected more than the POE oils. Once installed in a refrigeration or air conditioning system, PAG or POE oils are virtually impossible to completely remove from a system, especially from the compressor. If said systems where then recharged with chlorine containing refrigerants, such as R-406A or GHG-X4 and R-12 compatible mineral oils, some amount of the PAG or POE oils would remain and would be destroyed, creating contamination and system failures. A better performing refrigerant is needed that can be "drop-in" substituted for R-134a in R-134a refrigeration and air conditioning systems, and that is also compatible with oils used by R-134a refrigeration and air conditioning systems.
There are a few existing refrigerants that can be "drop-in" substituted for R-134a in R-134a refrigeration and airconditioning systems, such as OZ-12, HC-12a, and ES-12r. However, these mixtures are composed entirely of hydrocarbons (typically R-600a/290 40/60) and are extremely flammable. Hydocarbon mixtures are outlawed in many states and by US EPA as "unacceptable" for use as a replacement for R-12 in all but a few specialized uses. These hydrocarbon refrigerants contain no chlorinated compounds, so they do not destroy oils used in R-134a systems.